The present invention relates to a wheel bearing device for an automobile, and more particularly to a wheel bearing device having incorporated therein a mechanism that detects the number of rotations of a wheel of the automobile.
In an automobile equipped with an anti-skid braking system (ABS), it is necessary to detect the number of rotations of the wheels which changes moment by moment. A typical mechanism for detection of the number of rotations of the wheel is made up of a pulser ring having recessed and protruded teeth formed in an outer circumferential surface or a side thereof at a certain pitch, and a pickup sensor disposed so as to confront the recessed and protruded teeth for detection thereof.
A mechanism for detecting the number of rotations of the wheels of an automobile like the one described above is, as seen from a cross-sectional view illustrated in FIG. 2, incorporated in a wheel bearing device. In this example, an inner ring 21 is fixedly mounted to an axle S and acts as a fixed ring, and an outer ring 23, which is made to freely rotate relative to the inner ring 21 via rolling members, is fixedly mounted over a hub (not shown) of a wheel and acts as a rotating ring. In addition, a pulser ring 24 is mounted on the outer ring 23, i.e. the rotating ring, to thereby rotate together with the wheel. A pickup sensor 25 is supported on a fixed portion of the vehicle body via a carrier 26 and placed so as to contact the pulser ring 24.
A sealing member 24a made from rubber or the like is fixedly mounted on a radially innermost circumferential edge of the pulser ring 24, so that the sealing member 24a is brought into abutment with an outer circumferential surface of the inner ring 21 to achieve the sealing of the bearing. In addition, the pulser ring 24 and the pickup sensor 25 are sealed by a labyrinth seal 27 fixedly mounted on the side of the axle S.
In the wheel bearing device a for detecting the number of rotations of the wheel of an automobile as described above, although the seal 27 is mounted on the side of the axle S in an attempt to seal the pulser ring 24 and the pickup sensor 25, a gap G is still formed between the axle S or the seal 27 and each of the pulser ring 24 and the pickup sensor 25, which permits foreign matters to enter into the inside of the seal and adhere to the pulser ring 24 and the pickup sensor 25. This may interfere with the detection of the number of rotations.